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NEP1 orthologs encoding necrosis and ethylene inducing proteins exist as a multigene family in Phytophthora megakarya, causal agent of black pod disease on cacao

Published online by Cambridge University Press:  10 November 2005

Hanhong BAE
Affiliation:
USDA/ARS, Plant Sciences Institute, Sustainable Perennial Crops Laboratory, Beltsville Agricultural Research Center-West, Beltsville, MD 20705, USA. E-mail: rbae@asrr.arsusda.gov
John H. BOWERS
Affiliation:
USDA/ARS, Plant Sciences Institute, Sustainable Perennial Crops Laboratory, Beltsville Agricultural Research Center-West, Beltsville, MD 20705, USA. E-mail: rbae@asrr.arsusda.gov
Paul W. TOOLEY
Affiliation:
USDA/ARS, Foreign Disease-Weed Science Research Unit, Ft. Detrick, MD 21702-5023, USA.
Bryan A. BAILEY
Affiliation:
USDA/ARS, Plant Sciences Institute, Sustainable Perennial Crops Laboratory, Beltsville Agricultural Research Center-West, Beltsville, MD 20705, USA. E-mail: rbae@asrr.arsusda.gov
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Abstract

Phytophthora megakarya is a devastating oomycete pathogen that causes black pod disease in cacao. Phytophthora species produce a protein that has a similar sequence to the necrosis and ethylene inducing protein (Nep1) of Fusarium oxysporum. Multiple copies of NEP1 orthologs (PmegNEP) have been identified in P. megakarya and four other Phytophthora species (P. citrophthora, P. capsici, P. palmivora, and P. sojae). Genome database searches confirmed the existence of multiple copies of NEP1 orthologs in P. sojae and P. ramorum. In this study, nine different PmegNEP orthologs from P. megakarya strain Mk-1 were identified and analyzed. Of these nine orthologs, six were expressed in mycelium and in P. megakarya zoospore-infected cacao leaf tissue. The remaining two clones are either regulated differently, or are nonfunctional genes. Sequence analysis revealed that six PmegNEP orthologs were organized in two clusters of three orthologs each in the P. megakarya genome. Evidence is presented for the instability in the P. megakarya genome resulting from duplications, inversions, and fused genes resulting in multiple NEP1 orthologs. Traits characteristic of the Phytophthora genome, such as the clustering of NEP1 orthologs, the lack of CATT and TATA boxes, the lack of introns, and the short distance between ORFs were also observed.

Type
Research Article
Copyright
The British Mycological Society 2005

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